The Fineness of Grind Gage is a flat steel block in the surface of which are two flat-bottomed grooves varying uniformly in depth from a maximum at one end of the block to zero near the other end. Groove depth is graduated on the block according to the scales used for measuring particle size. The grind gages with extra deep groove are available either with "Microns - scale" or "Mils - scale".
Place a slight excess of sample in the deep end of the groove and, with the straight-edge scraper provided, draw the sample toward the shallow end of the groove. Ratings are in terms of the point on the scale where the oversize particles, or traces made by them, first appear in substantial concentration.